The majority of currently available speakers or electro-acoustic transducers comprise a moving membrane to transfer sound energy to the surrounding air. The mass of the moving membrane along with other nonlinearities (e.g. magnetic nonlinearity and suspension nonlinearities), introduces distortion/coloration into the sound.
In addition, due to the mechanics of the moving membrane, no currently available single speaker can adequately and efficiently cover the entire audio spectrum. It is therefore necessary to use a number of speakers in tandem to cover the entire audio spectrum (Woofer, Midrange, Tweeter). Using multiple speakers can result in significant overlap at different frequency ranges which also distorts the intended sound.
In order to overcome the issues with these known speakers, several attempts have been made to achieve a speaker which has an effective zero mass (except for the mass of the moving air). One method of creating a massless speaker is to use an atmospheric plasma to move the air.
An atmospheric plasma is most readily created by imposing a large electric field over a volume of air. The electric field causes a breakdown of the air molecules. Once the air molecules breakdown, they become ionized and will move in the direction of an applied electric field gradient. The moving ions will transfer their momentum to the surrounding air. By modulating the electric field, the air can be made move in time to an audio signal, thereby creating a sound wave.
Three known types of plasma speakers are:                Plasma Arc: these speakers use an electric arc which is modulated using an audio signal. An electric arc eventually breaks down due to erosion of the contacts caused by the high electric fields involved; further, the use of an electric arc is quite hazardous.        Tesla Coil: these speakers are based on the Tesla coil, they cause a lot of electrical interference and they are very impractical to commercialize.        Flame: these speakers use a flame (Bunsen burner) to create sound. By modulating the ions within the flame using an applied high voltage, sound can be generated. Again the commercialization of such a device is very difficult and the use of a flame is quite hazardous.        
While differing in their approach, generally it is considered that these kinds of plasma speakers are very impractical and have significant performance limitations, e.g. in frequency range and volume of the generated sound.
For example, none of these known plasma speakers are able to produce sufficient volume at the lower end of the audio spectrum (less than 2.5 kHz). Therefore, these plasma speakers have been restricted for use as Tweeters (High Frequency speakers).
A DBD (Dielectric Barrier Discharge) is a known device for producing a plasma between electrodes. The plasma is typically formed on an insulating surface between two parallel plate electrodes to which a large voltage is applied (greater than air breakdown electric field). DBD is primarily aimed at surface treatment to enhance wettability of materials preproduction or for surface sterilization in medical applications. DBD can be formed in air, other gas or at low pressure. Much of the research on DBD involves stabilizing the plasma formation (e.g. removal of micro discharges) to form a homogeneous plasma required for accurate surface treatment.
Plasma actuators are also known, which are derived from the DBD. The plasma actuators are devices for manipulating air flow using a pair of electrodes comprising one insulated, or encapsulated, electrode and one electrode exposed to air. An electric field is generated between the two electrodes which causes a motion of the air above to the actuator surface, in the direction of the electric field gradient (generally towards the insulated electrode). This airflow is a type of wall jet.
The airflow is generated by a momentum transfer from the plasma ions, moving along the lines of the electrical field, to the air close to the actuator.
Electroosmotic type flow model by Suzen (Numerical Simulations of Flow Separation Control in Low-Pressure Turbines using Plasma Actuators, Suzen, Y B, Huang, P G, Ashpis, D E, 45th AIAA Aerospace Sciences Meeting and Exhibit 8-11 Jan. 2007, Reno, Nev.), the Paraelectric flow model by Roth (The physics and phenomenology of paraelectric one atmosphere uniform glow discharge plasma (Oaugdp™) actuators for aerodynamic flow control, Roth, J Reece, Dai, Xin, Rahel, Jozef, Sherman, Daniel M, AIAA PAPER 2005-0781), and the model by Alonso Chirayath (Plasma Actuated Unmanned Aerial Vehicle, Chirayath, V, Alonso, Dr J. Stanford University, Dept of Physics, 2010, 2011, NASA Grant funded) involving different species ionization rates for positive/negative voltages, are examples of theories for explaining how the moving ions transfer a momentum to air.
According to the model by Suzen, electrons follow the electric field lines until they reach the surface of the insulator/air exposed electrode (depending on polarity). When they reach the insulator surface, they distribute to try to cancel the applied electric field. The ions are a lot slower and do not travel very far per AC cycle. According to this theory, the interaction between the insulator surface charge and the ions causes the momentum transfer to the air. The overall plasma volume is neutral within a ns timescale.
When the air exposed electrode is negative, electrons travel to the insulator surface and build up a surface charge. The surface charge redistributes in such a way to create a net momentum (caused by ions) away from the air exposed electrode.
When the air exposed electrode is positive, electrons migrate from the insulator surface to the air exposed electrode (following electric field lines) and ions move towards the insulator surface away from the air exposed electrode (nearly tangential to electric field lines). Ions are responsible for nearly all the momentum transfer. The momentum is usually not equal in both cycles; this creates a push/smaller push action on the air.
Plasma actuators are involved in flow control applications, mostly in aerospace (e.g. aircraft wings). By using the nonlinearity of an electric field across an atmospheric plasma, a flow is imparted to the surrounding air. This airflow can be used to reduce turbulence in the airflow over the actuator, by creating a suction/blowing effect over the plasma surface.
One of the primary limitations of the plasma actuators in flow control applications is the low speed of the generated airflow. The majority of research is aimed at enhancing the airflow speed, mostly through modification to: electrode gap size, electrode size, dielectric type, metal types, serrated electrodes, actuator voltage and frequency, AC voltage wave shape (sine, triangular, sawtooth, etc).
Several names are associated with plasma actuators: SDBD (Single Dielectric Barrier Discharge), sliding SDBD (where an additional AC or DC Voltage is used to increase force, at least marginally), OAUGDP (One Atmosphere Uniform Glow Discharge Plasma, used for example for surface treatment), Micro DBD (MEMs scale device). There are several modified air exposed electrode SDBD designs, e.g. serpentine or triangular designs (mainly directed to generation of micro vortex for air flow control).